The present invention relates generally to fault condition monitoring of printed circuit assemblies, such as those utilized within a digital computer, and specifically to the detection of the catastrophic failure of the dielectric in a multilayer printed circuit assembly, to the detection of the improper pluggable connection or non-connection of such a printed circuit assembly, and to the detection of temperature (over temperature) occurring on such printed circuit assembly. All such detections occur via a single signal wire, using system ground as the return.
Modern digital computers often use an array of multilayer printed circuit boards or assemblies to hold the digital logic components, interconnect them, and provide power to them. The amount of power used in such arrays of printed circuit assemblies is very high, on the order of tens of kilowatts. If a breakdown in the printed circuit dielectric between voltage and ground occurs, sufficient power is available to cause burning (carbonization) and potential fire on the failed printed circuit assembly. Such a catastrophic failure and fire may damage other closely spaced printed circuit assemblies.
The prior art burn detection method of smoke, or combustion product, detectors suffer from unreliability and a slow response time relative to the speed of the burn. Also previously utilized, overcurrent detection in power supplies is now insufficient to protect an individual printed circuit assembly. This is because the power supply may be outputting sufficient current to allow the catastrophic burn of an individual multilayer printed circuit assembly without such sufficient excess, or over, current as may be detected and utilized to protect such assembly. Finally, it would be possible to fuse each individual printed circuit assembly but such fusing is often inefficient or impractical. Fuses have a voltage drop and interfere with regulation of the d.c. voltage source. Fuses are physically large for the currents involved, approximately 100 amperes, and do not fit on a printed circuit board. Finally, if an individual printed circuit card assembly is fused at full circuit current, a burn may still occur and not blow the fuse.
As second and third aspects of the present invention the detection of an improper connection of a pluggable circuit assembly, and the temperature condition, including over temperature, occurring upon such printed circuit assembly will be detected upon a single signal wire, such single wire as is additionally utilized for the detection of catastrophic failure of the dielectric of the multilayer printed circuit assembly. Improper connection of a pluggable printed circuit assembly means that the connector(s) of such assembly, such as a linear plug, is (are) not physically correctly inserted to allow contacting the proper pins, or printed circuit lands, upon the printed circuit assembly. To the maximum extent possible, such improper plug connection of a printed circuit assembly is normally precluded by a physical design of the connectors so that improper mating is precluded. Insofar as electrical methods detect and verify the proper connection of a pluggable assembly, a check of the continuity through a first end pin of the connector, across a proscribed path upon the printed circuit assembly, and out an opposite end pin of the connector might be performed in order to demonstrate that the printed circuit assembly was properly plugged at least at each end of the connector. If one connected pin, possibly an end pin, is ground, then the proper occurrence of ground, as routed by the printed circuit assembly, upon another pin, possibly the other end pin, may be observed as an indication of correct connection. Finally, some signal(s) developable upon the printed circuit assembly only in the event of proper connection may be observed as an index (indices) of such proper connection. Should such electrical checks for proper connection be performed at all, they would not usually be perceived as being associated with either the sensing of temperature (detection of over temperature) nor the detection of the catastrophic failure of a dielectric in a multilayer printed circuit assembly.
Finally, the sensing of temperature (detection of over temperature) occurring upon a multilayer printed circuit assembly by the interrogation of a sensor, such as a thermocouple or thermistor, located upon such multilayer printed circuit assembly is old in the art. Normally, one port of a two port sensor is connected to either voltage of ground and only the signal resultant at the other port needs be routed from a pluggable multilayer printed circuit assembly for the external sensing of temperature occurring upon such assembly. When such a single wire connection is utilized for the sensing of temperature upon a printed circuit assembly, it is not normally associated with any additional purpose(s).